1. Field of the Invention
The present invention relates to a beam source suitable for use in a manufacturing process of semiconductor integrated circuits, information storage media such as hard disks, fine optical elements, micromachines, and the like, and more particularly to a beam source for generating various kinds of highly directional and highly dense beams including a positive ion beam, a negative ion beam, and a neutral particle beam from high-density plasma. The present invention also relates to a beam processing apparatus having such a beam source.
2. Description of the Related Art
In recent years, semiconductor integrated circuits, information storage media such as hard disks, fine optical elements, micromachines, and the like have been processed in highly fine patterns. In fields of processing such workpieces, attention has been attracted to use of a high-density energetic beam which is highly linear, i.e., highly directional, and has a relatively large beam diameter. For example, an energetic beam is applied to a workpiece to thereby deposit a film on the workpiece or etch the workpiece.
As beam sources of such energetic beams, there have been used beam generators which generate various kinds of beams including a positive ion beam, a negative ion beam, and a neutral particle beam. The positive ion beam, the negative ion beam, or the neutral particle beam is applied to a desired area of a workpiece from the beam source to thereby locally deposit a film on the workpiece, etch the workpiece, modify a surface of the workpiece, or join or bond parts of the workpiece together.
FIG. 1 shows a conventional beam processing apparatus having such a beam source. As shown in FIG. 1, the beam processing apparatus has a beam generating chamber 240 and a coil 220 disposed around the beam generating chamber 240 for inductively coupled plasma (ICP). The beam processing apparatus also has a first electrode 210 disposed at a lower end of the beam generating chamber 240 and a second electrode 250 disposed above the first electrode 210. The first electrode 210 and the second electrode 250 are made of an electrically conductive material such as graphite, respectively. When a high-frequency current is supplied from a high-frequency power supply via a matching box to the coil 220, an induced magnetic field is produced in the beam generating chamber 240 by the coil 220. The varying magnetic field induces an electric field, which accelerates electrons to generate plasma in the beam generating chamber 240. Thus, by applying a proper voltage between the first electrode 210 and the second electrode 250, various kinds of beams including a positive ion beam, a negative ion beam, and a neutral particle beam can be applied to a workpiece X.
For mass production and reduction in cost of semiconductor integrated circuits, fabrication apparatuses for semiconductor integrated circuits should be capable of processing workpieces having larger diameters. When the diameter of a conventional ion beam source is increased so as to generate various kinds of beams including a positive ion beam, a negative ion beam, and a neutral particle beam, the following problems arise.
In order to generate a uniform beam having a large diameter, it is desirable that the density of plasma, which is a source of a beam, should be distributed uniformly in radial and circumferential directions of the beam generating chamber. As shown in FIG. 1, in the conventional beam source, the coil 220 for inductively coupled plasma is disposed around the beam generating chamber 240. Accordingly, the energy supplied by the coil 220 is larger at a peripheral area and smaller at a central area in the beam generating chamber 240. Thus, the generated plasma tends to have a non-uniform density distribution in a radial direction of the beam generating chamber 240 so as to have higher densities at the peripheral area and lower densities at the central area in the beam generating chamber 240. When the beam generating chamber 240 has a diameter of about 100 mm, the coil 220 can supply sufficient energy to the central area of the beam generating chamber 240 so that the ununiformity of the plasma density is hardly caused. However, when the beam generating chamber 240 is increased in size to generate a beam having a larger diameter, the coil 220 cannot supply sufficient energy to the central area of the beam generating chamber 240. In such a case, the plasma density becomes non-uniform in the radial direction so as to make it difficult to generate a uniform beam.
Thus, in order to generate a uniform beam having a large diameter, it is necessary to generate uniform plasma having a large diameter. In order to generate such uniform plasma having a large diameter, there has been known to dispose a coil for inductively coupled plasma so as to face a workpiece.
In the conventional beam processing apparatus, charged particles such as positive ions or negative ions are applied to a workpiece unless a proper neutralization device is provided. In such a beam processing apparatus which applies charged particles to a workpiece, an insulated workpiece cannot be processed because of a charge build-up phenomenon in which electric charges are built up on the workpiece. Further, since the ion beam emitted from the beam source tends to spread due to the space-charge effect, the workpiece cannot be processed in a fine pattern.
In order to solve the above problems, there has been proposed a method of introducing electrons into the ion beam to neutralize the electric charges. This method can balance the electric charges on the workpiece as a whole. However, since local unbalance of the electric charges still remains on the workpiece, the workpiece cannot be processed in a fine pattern.
In the case where ions are extracted from a plasma source and applied to a workpiece, if a radiation (e.g. an ultraviolet ray) produced by the plasma source is applied to the workpiece, then the radiation adversely affects the workpiece. Thus, it is necessary to shield the workpiece from an adverse radiation (e.g. an ultraviolet ray) emitted from the plasma source.
Thus, it is desired to provide a beam source which can uniformly apply various kinds of beams including a positive ion beam, a negative ion beam, and a neutral particle beam so as to solve the aforementioned problems.
FIG. 2 shows a conventional neutral particle beam generating apparatus as disclosed by U.S. Pat. No. 6,331,701. As shown in FIG. 2, the neutral particle beam generating apparatus has an RF generator 291, an RF inductor 293 connected via an impedance matching device 292 to the RF generator 291, an RF window 294 disposed adjacent to the RF inductor 293, an RF accelerator 297 connected to an RF accelerator circuit 296, and an RF-grounded sub-Debye neutralizer grid 312 disposed so as to face the RF accelerator 297. The RF accelerator 297 is disposed so as to face the RF window 294.
With the above arrangement, RF power is supplied by the RF inductor 293 to generate plasma 295, 299. A potential difference is produced between the RF accelerator 297 and the sub-Debye neutralizer grid 312 to accelerate positive ions from the plasma 299 toward the sub-Debye neutralizer grid 312, which has grid holes 317. The accelerated positive ions are neutralized through the sub-Debye neutralizer grid 312 when they pass through the grid holes 317 in the sub-Debye neutralizer grid 312. Thus, the apparatus shown in FIG. 2 has a coil for inductively coupled plasma, which is disposed so as to face a workpiece in order to generate uniform plasma, a proper neutralization device, and a device for shielding radiation from being applied to the workpiece.
In order to generate a collimated beam having a high neutralization efficiency, the grid holes 317 in the sub-Debye neutralizer grid 312 should have a diameter smaller than the thickness of a sheath 311 formed between the plasma 299 and the sub-Debye neutralizer grid 312 and also should have a high aspect ratio of about 10. For these purposes, the manufacturing cost rises, and only limited materials can be used for the sub-Debye neutralizer grid 312. According to U.S. Pat. No. 6,331,701, aluminum is used for the sub-Debye neutralizer grid 312. However, because aluminum is likely to deform due to heat, it is an unsuitable material for a beam source having a large diameter of about 10 inches. Thus, it is difficult to generate a uniform beam having a large diameter with the neutral particle beam generating apparatus as disclosed by U.S. Pat. No. 6,331,701.